A “Wet Pipe Sprinkler System” is defined as a sprinkler system employing automatic sprinklers attached to a piping system containing water and connected to a water supply. Upon actuation of the automatic sprinkler in response to a fire, water is immediately discharged at a minimum designed, working or operating pressure to address the fire. As used herein, “operating pressure” is defined as the pressure required at the sprinkler head to achieve the designed performance objective of the sprinkler, e.g., standard spray, control mode, suppression, extended coverage, etc., under liquid flow conditions. The designed operating pressure preferably ranges from a minimum operating pressure, as preferably determined by industry accepted installation standards, such as for example the National Fire Protection Association (NFPA) standard, entitled “NFPA 13: Standards for the Installation of Sprinkler Systems” (2013 ed.) (“NFPA 13”), or the FM Global installation standard, to a maximum operating pressure as determined by the sprinkler designer or manufacturer or applicable standards. For example, NFPA 13 specifies a minimum operating pressure of 30 PSI for Control Mode Specific Application (CMSA) protection of Class I-IV rack storage over twenty-five feet in height with CMSA pendent sprinklers.
U.S. Pat. No. 7,857,069 (the “'069 patent”) is directed to methods of system valve actuation for a “deluge-like” wet pipe sprinkler system as shown and described in U.S. Patent Publication No. 2006/0289174 (the “'174 Publication”), which is directed to “deluge-like” sprinkler fire scheme using high thermal sensitivity and high temperature rating sensing elements. According to the '174 Publication, the “deluge-like” systems improve the fire protection performance of dry or controlled wet systems by purportedly preventing the problem of “sprinkler skipping.” These “deluge-like” systems operate by ensuring a designated number of automatic sprinkler actuations over a fire before operating a system fluid control valve for delivery of water from the actuated sprinklers at operating pressure. Essential to the overall system operation in reducing fire damage is the actuation of the system fluid control valve after or shortly before all sprinklers in a designated area above a small size fire have actuated in response to the fire so that the sprinklers in the designated area discharge at their designated operating pressure. According to the specification of the '174 Publication, valve operation and water application to the smaller size fires is made possible by the use of high thermally sensitive sprinklers (low RTI values 40-100 (ft-sec)1/2 [22-55 (meter-seconds)1/2]) with high temperature ratings (190°−650° F.).
The time at which a sprinkler actuates in response to a fire is determined, at least in part, by the sprinkler's temperature characteristics and more specifically its temperature rating and its thermal sensitivity. The nominal temperature rating of a thermally responsive trigger and its sprinkler defines the temperature range at which the sprinkler and its trigger will actuate. The thermal sensitivity of the sprinkler and its trigger is measured or quantified by the response time index (“RTI”) meter1/2 second1/2 (“m1/2 sec1/2”) as determined in a standardized test arrangement generally described in NFPA 13, in which the sprinkler is disposed within a test oven and exposed to a heated laminar airflow within the test oven. The RTI is calculated using the following: (i) the operating time of the sprinkler; (ii) the operating temperature (temperature rating) of the sprinkler; (iii) the air temperature of the test oven; (iv) the air velocity of the test oven; and (v) the conductivity between the sprinkler and its mount in the oven. According to NFPA 13, sprinklers are defined as “fast response” where its thermally responsive trigger has an RTI of 50 m1/2 sec1/2 or less. Sprinklers with an thermally responsive trigger having an RTI of 80 m1/2 sec1/2 or more are defined as “standard response.” Other standards recognize sprinklers having a thermally responsive trigger between 50 m1/2 sec1/2 and 80 m1/2 sec1/2 as “special response.” For commonality as used herein, a “fast response sprinkler” will refer to sprinkler having a thermally responsive trigger with an RTI of less than 80 m112 sec1/2; and “a standard response” is greater than 80 m1/2 sec1/2.
Again, in these known “deluge-like” systems no water is discharged at pressure from any actuated sprinkler until essentially all the designated sprinklers have been actuated. Fluid pressure is thus delayed in the system and methods of the '069 patent and the '174 Publication and system operation is reactive in the sense that the system operation is dependent upon a group of designated sprinkler actuations before operating the system fluid control valve. The '069 patent describes two methods of actuating the system fluid control valve of a “deluge-like” system to deliver the fluid pressure. Generally, the system valve is controlled open in response to a flow condition in the system piping following actuation of a designated number of sprinklers. More specifically, the operation of the system fluid control valve is based upon the designated number of sprinkler actuations that generate a threshold pressure drop and/or a threshold flow through the system piping. The preferred methods of operation require special piping arrangements, e.g. a bypass, and/or special piping sensor arrangements to detect the operative flow conditions. Because water pressure is delayed, the '174 indicates that the required number of system valves should be kept small or the thermal sensitivity of the system increased to ensure time operation of the system valve. Accordingly, there are limitations and or complexities in the implementation of these known “deluge-like” wet systems. Moreover, although the systems of the '069 patent and the '174 Publication address the issue of sprinkler skipping, the documents fail to provide methods and associated systems that allow for either a systematic approach for reducing total water flow or demand or for fire protection at ceiling heights not previously realized.
Therefore, there remains a need for wet systems that deliver fluid pressure to a group of thermally actuated sprinklers in which system delivery of fluid pressure is independent of the number of actual sprinkler actuations. Moreover, it is desirable to provide for systems and method of storage fire protection which have a total fluid flow demand that is less than known systems protecting similar storage configurations. Additionally, it is desirable to provide for storage fire protection at heights not yet available in known systems.